1. Field of the Invention
The present invention relates to a linear motor device, stage device, exposure apparatus, etc., more particularly relates to a stage device suitable for moving a mask (reticle), wafer, or other object for movement used in an exposure apparatus, a linear motor device suitable for realizing such a stage device, an exposure apparatus to which such a stage device is applied, etc.
2. Description of the Related Art
In the past, in lithography for producing a semiconductor element, liquid crystal display element, etc., use has been made of an exposure apparatus for transferring a pattern formed on a mask or reticle (hereinafter referred to all together as a xe2x80x9creticlexe2x80x9d) through a projection optical system on to a wafer, glass plate, or other substrate coated with a resist etc. (hereinafter suitably referred to as a xe2x80x9cphotosensitive substrate or waferxe2x80x9d). As such an exposure apparatus, use is mainly made of a so-called xe2x80x9cstepperxe2x80x9d or other stationary exposure type of projection exposure apparatus or so-called scanning stepper or other scanning exposure type of projection exposure apparatus. These types of projection exposure apparatuses have to successively transfer a pattern formed on the reticle to a plurality of shot areas on the wafer, so have been provided with wafer stages able to move two-dimensionally while holding the wafers. Further, scanning exposure types of projection exposure apparatuses have reticle stages which can move in the scanning direction while holding a reticle.
Recent projection exposure apparatuses use linear motors as the electromagnetic actuators used as drive sources in reticle stages, wafer stages, or other stage devices. This is because a linear motor is simple in structure, has fewer number of parts, has less frictional resistance in the drive and therefore a higher operational accuracy, and enables fast movement since it drives motion directly and linearly and therefore is suitable for answering the demands for improving the throughput or positioning accuracy of the reticle stage, wafer stage, etc.
The performance sought from an electromagnetic actuator for driving the wafer stage in a stationary exposure type of projection exposure apparatus can be summarized as follows:
(A) High speed, that is, how quickly the wafer can be made to move to a target position;
(B) High accuracy, that is, how accurately the wafer can be made to move to a target position; and
(C) Stability of stopping, that is, how stably a wafer can be stopped at the time of stopping it.
Further, the performance sought from the linear motor for driving the wafer stage in the scanning direction in a scanning exposure apparatus can be summarized as follows:
(D) High speed, that is, how quickly the wafer can reach a target position;
(E) Constant speed, that is, how fast and at how equal a speed the wafer can be scanned; and
(F) High accuracy, that is, whether the relative positional relationship between the wafer stage and reticle stage can be maintained at a predetermined positional relationship.
Various linear motors have been developed to satisfy these many demands on performance. In general, a linear motor is comprised of a stator fixed to a predetermined member and a movable member fixed on a member moving with respect to that predetermined member. Where the stator includes coils, the movable member includes permanent magnets and other magnets. Where the stator includes magnets, the movable member includes coils. A linear motor in which magnets are included in the movable member and coils are included in the stator is called a xe2x80x9cmoving magnet typexe2x80x9d, while a linear motor in which coils are included in the movable member and magnets are included in the stator is called a xe2x80x9cmoving coil typexe2x80x9d.
A reticle stage or wafer stage in an exposure apparatus, however, requires accurate positioning, so when a linear motor is used, the problem sometimes arises of the heat generated by the coils causing minute changes in temperature which the affect the accuracy of the surrounding devices. For example, the heat generated by the coils sometimes causes fluctuations in the gas in the surrounding atmosphere and a reduction in the accuracy of position measurement by a laser interferometer. Further, along with the increase in size of the device produced, the reticle stage or wafer stage also becomes larger in size and greater in weight. Therefore, a linear motor with a large thrust has become desired for driving a reticle stage or wafer stage.
To increase the thrust of a linear motor, it may be considered to (1) increase the number of turns of the armature coil, (2) supply a large current to the armature coil, (3) increase the magnetic force of the permanent magnets, etc. These conditions, however, are mutually restrictive, so it becomes necessary to set the optimum conditions. For example, if increasing the number of turns of the armature coil for increasing the thrust, that many more airgaps become required. The thrust does not increase proportionally to the increase in the number of turns. To increase the number of turns without changing the airgaps, it is possible to reduce the diameter of the conductors of the coils, but if the diameter is reduced, the resistance rises. An increase in number of turns also raises the resistance. Therefore, the amount of heat generated becomes greater. Even if increasing the current, the amount of heat generated similarly becomes larger. If the size or scale of the linear motor is determined in this way, the maximum current, number of turns, resistance of the armature coil, airgaps, and other conditions are also determined. There have therefore been limits to increasing the thrust by such changes.
To remove the heat generated from the coils, it is known to provide cooling pipes around the coils or use heat insulating materials for blocking the transmission of the heat. With these methods, however, there have been problems of an inability to obtain the stability of temperature required for accurate positioning in an exposure apparatus or an increase in the size of the apparatus.
Further, when a large current is required for obtaining a high thrust, with the above conventional methods, a large amount of a refrigerant had to be circulated at a high speed or the cooling passage had to be made larger. High speed circulation of a refrigerant requires use of a high pressure circulation pump and places a load on the welds or joins of the circulation route and may lead to accidents such as leakage of the refrigerant.
An object of the present invention is to provide a linear motor device able to give a large thrust without increasing the amount of generation of heat.
Another object of the present invention is to provide a stage device able to realize high precision movement or positioning.
Still another object of the present invention is to provide an exposure apparatus with a high exposure accuracy.
Still other objects of the present invention will become clear from the following description.
According to a first aspect of the present invention for achieving the above object, there is provided a linear motor device comprising a movable member, a stator having coils, and a control system for powering selected coils among the coils in accordance with a position of the movable member. According to this configuration, since the control system for powering coils selected in accordance with the position of the movable member is employed, for example it becomes possible to power just coils interacting with the movable member and therefore enable efficient driving and possible to obtain a large thrust without increasing the amount of heat generated.
According to a second aspect of the present invention for achieving the above other object, there is provided a stage device comprising a linear motor device and stage, the linear motor device including a movable member, a stator having coils, and a control system for powering selected coils among the coils in accordance with a position of the movable member, and the stage being connected to the movable member. Due to this configuration, in accordance with the present invention, it is possible to keep down the amount of generation of heat of the linear motor, so it is possible to improve the accuracy of position measurement by means of a laser interferometer because of preventing the fluctuations of the gas in the atmosphere around the stage and further possible to keep down the heat expansion of the stage and other peripheral parts and as a result improve the movement or positioning accuracy of the stage.
According to a third aspect of the present invention for achieving the still other object, there is provided an exposure apparatus for exposing a photosensitive substrate through a mask formed with a pattern, comprising a stage device for moving at least one of the mask and photosensitive substrate, the stage device being provided with a linear motor device including a movable member, a stator having coils, and a control system for powering selected coils among the coils in accordance with a position of the movable member and a stage connected to the movable member. According to this configuration, since the movement and positioning accuracy of the stage is high, it becomes possible to transfer an image of the pattern formed on the mask to the photosensitive substrate with a good accuracy.